Demanding Pres Trump to Release Tax Returns

Someone tell me where releasing Tax Returns is a requisite to run for President because I am unaware of it. What I am aware is that for any office the requirements include proof of age, citizenship (Pres must be natural born), residence.

So what did we have about Barack Obama? Before he ran for Pres he was an Illinois State Senator. I feel assured that the had the same requirements. Therefore, when the big todo about his birth certificate started why was not his proof from running for IL State Senator. That would by default prove his age and where he was born and could have been used for the public record and ended the nonsense before he started.

I believed him but now do not. As Pres he could have forced someone or enabled a false document.